Recently, with a growing number of mobile stations such as mobile phones and WLANs (Wireless Local Area Networks), there are growing social demands for the effective utilization of frequency resources. Spatial multiplexing scheme is one of the communication schemes that meet these demands. Spatial multiplexing scheme is a scheme of communicating transmission and reception signals of multiple mobile stations in a multiplexing manner at the same frequency and at the same time by forming directivity patterns that are different for each of the mobile stations by using an adaptive array antenna apparatus.
An adaptive array antenna apparatus is provided with multiple wireless units, each comprising an antenna, a transmission unit, and a reception unit, and forms directivity patterns as a whole by adjusting the amplitudes and phases of reception signals and transmission signals input into or output from the wireless units. Directivity patterns are formed by weighting reception signals and transmission signals input into or output from the wireless units by weight vectors for adjusting the amplitudes and phases.
However, regarding an LNA (Low Noise Amplifier) in the reception unit, an HPA (High Power Amplifier) in the transmission unit, etc., the transmission unit and the reception unit can have different characteristics of transmission among antennas such as the amount of phase rotation or the amount of amplitude fluctuation of a signal due to the individual difference or the temperature change under the environment of usage. Such differences in the transmission characteristics between the reception unit and the transmission unit affect the formation of a directivity pattern during reception and transmission.
For this reason, a calibration process needs to be performed for obtaining the difference in transmission characteristics between the transmission unit and the reception unit and compensating for the difference in transmission characteristics. In the related art, a desired signal and an interference signal are separately transmitted from two signal sources and superimposed by a synthesizer. A calibration process is then performed based on the superimposed signal in a wireless apparatus (e.g., patent document 1). [Patent document 1] JP 2001-352282